DSpace at VNU: Synthesis of PtRu C-CNTs electrocatalysts for DMFCs with treated-CNTs and composition regulation

Home Search Collections Journals About Contact us My IOPscience Synthesis of PtRu/C-CNTs electrocatalysts for DMFCs with treated-CNTs and composition regulation This content has been downloaded from IOPscience Please scroll down to see the full text 2014 Adv Nat Sci: Nanosci Nanotechnol 035015 (http://iopscience.iop.org/2043-6262/5/3/035015) View the table of contents for this issue, or go to the journal homepage for more Download details: IP Address: 198.91.37.2 This content was downloaded on 21/02/2015 at 03:18 Please note that terms and conditions apply | Vietnam Academy of Science and Technology Advances in Natural Sciences: Nanoscience and Nanotechnology Adv Nat Sci.: Nanosci Nanotechnol (2014) 035015 (6pp) doi:10.1088/2043-6262/5/3/035015 Synthesis of PtRu/C-CNTs electrocatalysts for DMFCs with treated-CNTs and composition regulation Long Quan Dang1,2,3, Manh Tuan Nguyen2, Viet Long Nguyen3,5,6, Minh Thi Cao4, Van Thang Le7, Le Hoai Phuong Nguyen8, Ngoc Phuong Nguyen2, Thanh Hoang Nguyen2 and Thi Nga Do2 College of Natural Sciences, Can Tho University, Ninh Kieu District, Can Tho City, Vietnam Ho Chi Minh City Institute of Physics, 01 Mac Dinh Chi, District 1, Ho Chi Minh City, Vietnam Laboratory for Nanotechnology, Vietnam National University in Ho Chi Minh City, Community 6, Linh Trung Ward, Thu Duc District, Ho Chi Minh City, Vietnam Ho Chi Minh City University of Technology, 144/24 Dien Bien Phu, Ward 25, Binh Thanh District, Ho Chi Minh City, Vietnam Posts and Telecommunications Institute of Technology, km 10 Nguyen Trai, Hanoi, Vietnam Shanghai Institute of Ceramics, Chinese Academy of Science, 1295, Dingxi Road, Shanghai 200050, People’s Republic of China Ho Chi Minh City University of Technology, District 10, Ho Chi Minh City, Vietnam Tay Do University, Cai Rang District, Can Tho City, Vietnam E-mail: dlquan@ctu.edu.vn, manhtuan2k@yahoo.com and nguyenviet_long@yahoo.com Received 14 March 2014 Accepted for publication 18 August 2014 Published September 2014 Abstract In the present work, PtRu/C-CNTs catalyst samples were studied for potential applications in direct methanol fuel cells (DMFCs) Carbon nanotubes (CNTs) were treated by H2SO4 98% and HNO3 65% at different temperatures and with different stirring periods As a result, the PtRu/CCNTs catalyst was successfully synthesized by using H2PtCl6 and RuCl3 precursors with the efficient reduction of NaBH4 agent in ethylene glycol (e.g.) In addition, we controlled the ratios of treated-CNTs on carbon vulcan XC-72 treated-CNTs substrate (C-CNTs) with the different values: 50 wt%, 25 wt%, and 12.5 wt%, respectively The PtRu/C-CNTs electrocatalyst samples were investigated by experimental methods including x-ray diffraction (XRD), transmission electron microscopy (TEM), and cyclic voltammetry (CV) Importantly, the CV results show the best treated-CNTs and the most suitable ratio of CNTs composition on C-CNTs substrate to be controlled in order to produce various efficient PtRu/C-CNTs catalysts with high catalytic activity for DMFCs Keywords: carbon nanotubes, direct methanol fuel cells, PtRu/C-CNTs electrocatalyst MSC numbers: 5.06 Introduction operation principle [3]: Anode: CH 3OH + H O → CO2 + 6H + + 6e− , Cathode: O2 + 6H + + 6e− → 3H O, Overallreaction: CH 3OH + O2 → CO2 + 2H O Fuel cells (FCs) are recognized as promising energy power sources for the future [1] Among various FCs, direct methanol fuel cells (DMFCs) are known as a low operation temperature cell, using methanol fuel and the membrane–electrode assembly (MEA) technology [2] The Pt based catalysts are used in the electrodes of DMFCs, following 2043-6262/14/035015+06$33.00 © 2014 Vietnam Academy of Science & Technology Adv Nat Sci.: Nanosci Nanotechnol (2014) 035015 L Q Dang et al However, the Pt catalyst is easily poisoned by carbon monoxide (CO) which was produced from hydrogen oxidation reaction (HOR) This problem is solved by using Pt–Ru based catalysts The Ru metal composition will reduce CO in Pt–CO bondings as follows [2]: Ru + H O → Ru − OH + H + + e− , Ru − OH + Pt − CO → Pt + Ru + CO2 + H + + e− Conventionally, highly conductive carbon blacks, such as vulcan XC-72, are used as supports for Pt electrocatalysts After the discovery of carbon nanotubes (CNTs) [4], Pt/CNTs based catalysts were investigated by many authors [1, 5–11] Before the use of CNTs, they must be treated in strong acids, such as HNO3 or a mixture of HNO3 and H2SO4, at a temperature and a period value to remove impurities and generate amounts of functional groups, e.g., –OH, –COOH, –C = O on the CNTs surfaces [1] However, there are significant differences about temperatures and periods treated between authors For example, Li et al refluxed CNTs in 70% HNO3 at 120 °C for h and then treated them in a 4.0 N H2SO4–HNO3 mixture for h [5]; Zhao et al purified MWNTs by refluxing them with 60% HNO3 at 90 °C for h and then the surface oxidation of the MWNTs was carried out by refluxing MWNTs in M H2SO4 + M HNO3 at 90 °C for h [7], the group of Lee treated CNTs for 36 h at 110 °C in a mixed solution of HNO3 and H2SO4 [11], and so forth [1, 8–10] Besides, the effect of the ratio of CNTs composition on CCNTs substrate on quality of PtRu/C-CNTs electrocatalyst has not been studied so far In this work we have prepared PtRu/C-CNTs catalyst samples using many types of CNTs that were treated at different temperatures and with different stirring periods Besides, we have also prepared PtRu/C-CNTs electrocatalyst samples using different ratios of treated-CNTs Our purpose is to find out the best treated-CNTs sample and the best ratio of treated-CNTs for PtRu/C-CNTs electrocatalysts Figure The image of CNTs, supplied by producer Table Data sheet of CNTs, supplied by producer Properties Value C-purify Outer diameter Inner diameter Length >95 wt% 1 μm Table CNTs treatment samples Sample name PtRu/C-CNTs PtRu/C-CNTs PtRu/C-CNTs PtRu/C-CNTs PtRu/C-CNTs PtRu/C-CNTs Temperature 01 02 03 05 06 07 Room 50 °C 50 °C 100 °C 100 °C Room Time (hours) 5 10 10 10 Experimental 2.1 CNTs treatment The CNTs material in our work was manufactured by Ho Chi Minh City University of Technology, Vietnam Parameter and image of CNTs are shown in figure and table In our experiments on treated-CNTs (called experiment 1), CNTs samples were dissolved in H2SO4 98%–HNO3 65% mixture with the volume ratio 1:1 under ultrasonic treatment for 15 They were refluxed at temperatures and with stirring periods, as presented in table In the experiment on the ratio of CNTs composition with C-CNTs substrate (called experiment 2), CNTs sample was dissolved in H2SO4 98% + HNO3 65% with the volume ratio 1:1 under ultrasonic treatment for 15 This mixture was then stirred at room temperature for h After h, activated CNTs were washed by centrifugal filter method to remove acid impurities Finally, it was dried at 100 °C under vacuum condition for several hours Figure XRD pattern of PtRu/C-CNTs catalyst sample Adv Nat Sci.: Nanosci Nanotechnol (2014) 035015 L Q Dang et al Figure TEM images of PtRu/C-CNTs catalyst samples (a): PtRu/C-CNTs 03 sample; (b): PtRu/C-CNTs 06 sample; (c): PtRu/C-CNTs 23 sample; and (d): PtRu/C-CNTs 24 sample (see also tables and 3) Table Ratios of treated-CNTs in different PtRu/C-CNTs samples Sample name Carbon vulcan mass (mg) CNTs mass (mg) 20 30 35 20 10 PtRu/C-CNTs 23 PtRu/C-CNTs 24 PtRu/C-CNTs 25 Ratio of CNTs 50% 25% 12.5% Table The result of CV investigation of PtRu/C-CNTs 2.2 Preparation of PtRu/C-CNTs electrocatalysts electrocatalyst samples 2.2.1 Experiment (on treated-CNTs) Firstly, we have used mg activated CNTs, 36 mg carbon vulcan XC-72 (10% CNTs), 10 ml acid H2SO4 98%, and 40 ml ethylene glycol Their mixture was treated by ultrasonic method for 15 Then the mixture was stirred at 150 °C for 30 After that, the precursor of PtRu (H2PtCl6.6H2O and RuCl3.xH2O solution) was added Here, atomic ratio of Pt:Ru was equal to 1:1 The ratio of PtRu composition with 20 wt% on PtRu/ C-CNTs was controlled in all samples Next, 0.4 g NaBH4 and 20 ml DI water solution was sprinkled into the mixture The pH was adjusted to about 12 by using NaOH The mixture was stirred at room temperature for h It was dried at 100 °C under vacuum condition for several hours Finally, we gained the PtRu/C-CNTs electrocatalyst sample Sample name PtRu/C-CNTs PtRu/C-CNTs PtRu/C-CNTs PtRu/C-CNTs PtRu/C-CNTs PtRu/C-CNTs 01 02 03 05 06 07 If (A cm−2) Ir (A cm−2) If/Ir 0.03 145 0.02 034 0.02 086 0.01 554 0.06 150 0.05 323 0.01 048 0.00 553 0.00 150 0.00 155 0.02 557 0.02 804 3.0 3.7 13.9 10.0 2.4 1.9 below (table 3) Next, these samples were treated by ultrasonic method in 10 ml acid H2SO4 98% and 40 ml ethylene glycol solution for 15 min, then they were stirred at 150 °C for 30 After that, the precursor of PtRu, H2PtCl6.6H2O and RuCl3.xH2O solution (atomic ratio Pt: Ru = 1:1, the ratio of PtRu composition with 20 wt% on PtRu/C-CNTs was controlled in all samples) was added Solution of 0.4 g NaBH4 and 20 ml DI water was sprinkled 2.2.2 Experiment (on the ratio of CNTs composition with CCNTs substrate) Firstly, mixtures of activated CNTs and carbon vulcan XC-72 were produced following the ratios Adv Nat Sci.: Nanosci Nanotechnol (2014) 035015 L Q Dang et al Figure CV of PtRu/C-CNTs electrocatalyst samples (a) PtRu/C-CNTs 01 sample; (b) PtRu/C-CNTs 07 sample; (c) PtRu/C-CNTs 02 sample; (d) PtRu/C-CNTs 03 sample; (e) PtRu/C-CNTs 05 sample and f) PtRu/C-CNTs 06 sample into mixtures The pH was adjusted to about 12 by using NaOH Mixtures were stirred for h at room temperature Finally, they were dried at 100 °C under vacuum condition for several hours We gained PtRu/C-CNTs electrocatalyst samples All of PtRu/C-CNTs electrocatalyst samples were investigated by x-ray diffraction (XRD), transmission electron microscopy (TEM) and cyclic voltammetry (CV) mg PtRu/C-CNTs electrocatalyst on cm2 Toray carbon paper and it was a working electrode in CV system CV investigation was performed on PARSTAT 2273 system using 0.5 M H2SO4 + 1.0 M CH3OH solution, with a sweep rate of 50 mV s−1 2.3 Electrochemical investigation on methanol electrooxidation 3.1 XRD and TEM characterizations Results and discussion XRD spectrum of a typical PtRu/C-CNTs catalyst sample was surveyed in figure It has four diffraction peaks at the angle 2θ of 39.7°, 46.3°, 67.9° and 81.6° corresponding to the surface (111), (200), (220) and (311), respectively These Electrochemical investigation on methanol electro-oxidation of PtRu/C-CNTs samples was carried out by cyclic voltammetry Each PtRu/C-CNTs sample was prepared by coating Adv Nat Sci.: Nanosci Nanotechnol (2014) 035015 L Q Dang et al Figure Comparison between CV couples at the same temperature a) PtRu/C-CNTs 01 sample versus PtRu/C-CNTs 07 sample; b) PtRu/CCNTs 02 sample versus PtRu/C-CNTs 03 sample and c) PtRu/C-CNTs 05 sample versus PtRu/C-CNTs 06 sample Figure CV of PtRu/C-CNTs electrocatalyst samples a) PtRu/C-CNTs-23 sample; b) PtRu/C-CNTs 24 sample; c) PtRu/C-CNTs 25 sample peaks are characteristic of the fcc structure of platinum According to Sherrer’s formula, the average size of PtRu nanoparticles is about 5.2 nm Figure presents a typical sample of PtRu/C-CNTs nanoparticles It clearly shows that PtRu nanoparticles were made up on CNTs and carbon vulcan with a high homogeneousness 3.2 Cyclic voltammetry investigation 3.2.1 Experiment (on treated-CNTs) CV investigation of PtRu/C-CNTs electrocatalyst samples is presented in figure According to previous results [12], the oxidation of methanol is observed in the forward scan at point A, and an oxidation peak in the reverse scan at point B, which is attributed to the Adv Nat Sci.: Nanosci Nanotechnol (2014) 035015 L Q Dang et al highest value (77.09 mA cm−2), while the If of PtRu/C-CNTs 25 sample (ratio of CNTs 12.5 wt%) is the lowest (15.78 mA cm−2) From table 5, the lowest and highest value of If/Ir ratio are 2.25 and 27.21 for the sample PtRu/C-CNTs 24 and PtRu/ C-CNTs 25, respectively This means the PtRu/C-CNTs 25 sample (ratio of CNTs 12.5 wt.%) has the best CO tolerance Despite the PtRu/C-CNTs 25 sample having the highest value of If/Ir ratio, it methanol oxidation ability has the lowest value Hence, we make the choice between the PtRu/C-CNTs 23 sample and the PtRu/C-CNTs 24 sample In this case, the PtRu/C-CNTs 24 sample has methanol oxidation ability superior to that of PtRu/C-CNTs 23 sample but their If/Ir ratio is similar, 2.94 and 2.25, respectively (figure and table 5) Figure Comparison between PtRu/C-CNTs_23 sample and PtRu/ C-CNTs_24 sample Conclusion Table The result of CV investigation of PtRu/C-CNTs PtRu/C-CNTs electrocatalyst was successfully synthesized by using of H2PtCl6 and RuCl3 precursors with the reduction of NaBH4 agent in ethylene glycol with high homogeneousness In the first experiment, PtRu/C-CNTs electrocatalyst samples using CNTs were treated by H2SO4 98% and HNO3 65% at different temperatures and with different stirring periods We also synthesized PtRu/C-CNTs electrocatalyst samples using different ratios of treated-CNTs in the second experiment The results showed that the methanol oxidation ability of samples under stirring for 10 h was always higher than samples under stirring for h In addition, the sample stirred at 100 °C for 10 h has the highest methanol oxidation ability The CV results also show that the methanol oxidation ability of PtRu/C-CNTs 24 sample (ratio of CNTs 25 wt%) is far superior compared with other samples Therefore, it may be the best choice sample of PtRu/C-CNTs electrocatalyst for DMFCs electrocatalyst samples Sample name PtRu/C-CNTs 23 PtRu/C-CNTs 24 PtRu/C-CNTs 25 −2 −2 If (A cm ) Ir (A cm ) If/Ir 0.02 808 0.07 709 0.01 578 0.00 956 0.03 429 0.00 058 2.94 2.25 27.21 removal of the incompletely oxidized carbonaceous species formed in the forward scan These carbonaceous species are mostly in the form of linearly bonded Pt − C ≡ O [13] The result of CV investigation also shows a wide difference between samples, presented in table Table provides the value of peak current density of the methanol oxidation peak in the forward scan (If) and the reverse scan (Ir) of PtRu/C-CNTs electrocatalyst samples It clearly shows that the If of PtRu/C-CNTs 06 sample (strirred for 10 h at 100 °C) receives the highest value, 61.5 mA cm−2 It also proves that If value of samples under strirring for 10 h is higher than that of samples under strirring for h at the same temperature, this is confirmed by figure The ratio of the forward peak current density to the reverse peak current density (If/Ir) can be used to describe the issue of catalyst tolerance to CO accumulation [12, 13] From table 4, the lowest and highest values of If/Ir ratio are 1.9 and 13.9 for the sample PtRu/C-CNTs 07 and PtRu/C-CNTs 03, respectively It means that PtRu/C-CNTs 03 sample (strirred for 10 h at 50 °C) has the best CO tolerance References [1] Jeng K, Chien C, Hsu N, Yen S, Chiou S, Lin S and Huang W 2006 J Power Sources 160 97 [2] Long N V, Thi C M, Yong Y, Nogami M and Ohtaki M 2013 J Nanosci Nanotechnol 13 4799 [3] Hoogers G 2003 Fuel Cell Technology Handbook (Boca Raton, FL: CRC Press) [4] Iijima S 1991 Nature 354 56 [5] Li W, Liang C, Qiu J, Zhou W, Han H, Wei Z, Sun G and Xin Q 2002 Carbon 40 791 [6] Wang C, Waje M, Wang X, Tang J M, Haddon R C and Yan Y 2004 Nano Lett 345 [7] Prabhuram J, Zhao T S, Liang Z X and Chen R 2007 Electrochim Acta 52 2649 [8] Wu G and Xu B Q 2007 J Power Sources 174 148 [9] Jha N, Reddy A L M, Shaijumon M M, Rajalakshmi N and Ramaprabhu S 2008 Int J Hydrogen Energy 33 427 [10] Xu J, Hua K, Sun G, Wang C, Xiangyu L and Wang Y 2006 Electrochem Commun 982 [11] Lee T K, Jung J H, Kim J B and Hur S H 2012 Int J Hydrogen Energy 37 17992 [12] Naidoo Q, Naidoo S, Petrik L, Nechaev A and Ndungu P 2012 Int J Hydrogen Energy 37 9459 [13] Liu Z and Hong L 2007 Electrochem 37 505 3.2.2 Experiment (on the ratio of CNTs composition with CCNTs substrate) CV investigation of PtRu/C-CNTs electrocatalyst samples in this experiment is presented in figure and the result of CV investigation shows a wide difference between samples presented in table Similarly to experiment 1, table provides the value of peak current density of the methanol oxidation peak in the forward scan (If) and the reverse scan (Ir) of PtRu/C-CNTs electrocatalyst samples The table clearly shows that the If of PtRu/C-CNTs 24 sample (ratio of CNTs 25 wt%) receives the ... 20 10 PtRu/ C-CNTs 23 PtRu/ C-CNTs 24 PtRu/ C-CNTs 25 Ratio of CNTs 50% 25% 12.5% Table The result of CV investigation of PtRu/ C-CNTs 2.2 Preparation of PtRu/ C-CNTs electrocatalysts electrocatalyst... using different ratios of treated-CNTs Our purpose is to find out the best treated-CNTs sample and the best ratio of treated-CNTs for PtRu/ C-CNTs electrocatalysts Figure The image of CNTs, supplied... CV of PtRu/ C-CNTs electrocatalyst samples (a) PtRu/ C-CNTs 01 sample; (b) PtRu/ C-CNTs 07 sample; (c) PtRu/ C-CNTs 02 sample; (d) PtRu/ C-CNTs 03 sample; (e) PtRu/ C-CNTs 05 sample and f) PtRu/ C-CNTs